A Critical Review on Quercetin Bioflavonoid and its Derivatives: Scope, Synthesis, and Biological Applications with Future Prospects

Lifestyle is an important factor in health, and researchers are trying to see the adverse effect on human health of a change in lifestyle. Many people follow unhealthy lifestyles, which affect human physical and mental health. Millions of people suffer from various problems like cardiovascular disease, overweight, malnutrition, hypertension, stress, violence, etc. There are many medicines that can cure these diseases, but they have side effects. When a man consumes green leaves and vegetables in his diet, his chances of reducing the risk of any disease increase. Every plant has primary and secondary metabolites. Flavonoid is a secondary metabolite found in various plants that plays an important role in the survival of the plant by performing physiological activities and being able to withstand adverse effects from the environment. Quercetin is one such bioflavonoid found in many plants, like onions, citrus fruits, parsley, etc. It comes under the category of flavone, with five hydroxy groups and a chromen-4-one skeletal structure. It has various applications, which include anti-cancer, anti-bacterial, anti-viral, anti-inflammatory, anti-diabetic, etc. However, the use of quercetin is limited due to its poor bioavailability, poor aqueous solubility, lower stability in the gastrointestinal tract, and first-pass effect. To enhance the application of quercetin, various derivatives of quercetin and its metal complex are required that are water soluble, which helps them reach the target site without any first-pass effect and provides them with stability. This review is divided into three main sections: The first section explains about flavonoids and their types; the second section explains about quercetin, its various methods of synthesis, its derivatives, and its metal complex; and the last section represents the complete applications of quercetin, with the drawbacks and how to overcome or deal with the drawbacks.